This invention relates to selective detection of vapors and more particularly to improved high speed gas chromatographic analyses for detecting vapors of specific compounds, especially certain nitrogen-containing compounds.
Chromatography is commonly utilized to provide timewise separation of constituents of gas or liquid samples as part of analyses in which specific compounds are detected. The timewise separation achieved among constituents permits particular compounds to be distinguished from potential interferents and from other specific compounds of interest by signal peaks which occur at distinct times as the output of detectors downstream of the gas or liquid chromatograph. The times of interest, and amplitude and even shape of the signals of interest, can be predetermined by calibrations using samples of known composition, and detection systems containing the chromatographs can be electronically programmed to provide alarms of specific responses upon detection of each compound of interest.
Gas chromatographic (GC) systems have proven quite useful in analysis of samples containing vapors or gases of unknown composition. Recently-developed GC systems can separate and detect certain substances within a sample rather quickly and accurately. However, further improvements are desirable, particularly in the selectivity and sensitivity of such GC systems.
Accordingly, it is an object of the invention to provide as improved high speed vapor detection GC system and method.
It is an object of the invention to provide an improved system for selectively detecting specific nitrogen-based compounds.
It is an object of the invention to provide a high speed GC vapor detector which detects different sets of compounds during multiple time intervals and which time shifts the detection of at least one set.
It is a particular object of the invention to provide a high speed vapor detector configured to detect different compounds during two discrete intervals of time and having improvements which eliminate potential interferents during at least one of the detection intervals.
It is also an object of the invention to provide a highly selective and sensitive apparatus and method for improved high speed detection of vapors of nitro-compounds such as explosives.
It is also an object of the invention to provide a method and apparatus for rapidly and precisely controlling the temperature of current-carrying elements such as metal tube casings of components of a high speed GC vapor detector.